Semi-conductor electrode system



P 3, 1957 A. VAN WIERINGEN 2,805,369

SEMI-CONDUCTOR ELECTRODE SYSTEM Filed Aug. 14, 1955 1 1 I I!!! I 1 1 1 111 f ff .11 1 1 111 1 11 1 1111 1/ I l I INVENTOR ADRlANUS VAN WIERINGEN AGENT Patented Sept. 3, 1957 SEMI-CONDUCTOR ELECTRODE SYSTEMAdrianus van Wieringen, Eindhoven, Netherlands, as-

signor, by mesne assignments, to North American Philips Company, lnc.,New York, N. Y., a corporation of Delaware Application August 14, 1953,Serial No. 374,209

Claims priority, application Netherlands August 27, 1952 2 Claims. (Cl.317236) The invention relates to semi-conductors, and, in particular, toelectrode systems for granular semi-conductors, such as crystal diodesor transistors.

A known method of manufacturing granular semiconducting bodies, e. g.,of germanium or silicon, results in a more or less egg-shaped body, thenarrow top of which has a much higher concentration of impurities thanthe wider lower portion, that is to say, the impurities in thesemi-conducting body which adversely affect its elec tric properties,for example, its rectifying properties, are lumped in the top of thebody or grain. In British Patent No. 683,248, it has been proposed tomount the eggshaped body with the top projecting outwardly from themetallic support and to remove the top with its undesirable impuritiesto form a contact surface.

The present invention is based on the discovery that it is possible totake advantage of the presence of these undesirable impurities bysecuring the narrow top of the body to a base electrode, since arectifying junction at this area is undesirable. The electrode systemaccording to the invention, therefore, comprises an egg-shapedsemiconducting body, the narrow end of which has a higher concentrationof impurities than the wider end. A good electrical ohmic connection iseffected to the narrow end, i. e., it is secured to a base electrode,and the wider end is flattened, e. g., by grinding, for the purpose ofeffecting a rectifying connection thereto.

The advantage of the construction according to the invention is that,not only are the impurities in the semiconductor arranged in a zone inwhich they are not harmful, but their presence is actually utilized toreduce the contact resistance to the base. It is preferred that theflattened, wider part of the egg-shaped body contains no impurities, i.e., it consists solely of pure semi-conducting material, since thisreduces the risk that this surface may become contaminated.

The invention will now be described with reference to the accompanyingdiagrammatic drawing in which the single figure is a sectional view ofone embodiment of the invention.

Referring now to the drawing, the electrode system of the inventioncomprises a rod-shaped base electrode 1 provided with a supply conductor2 and having a granular semi-conducting body 3 secured to it by means ofsolder 4. The body is egg-shaped and has its head on the top portion 5adjacent the base 1. Its wider upper end 6 is flattened, for example, bygrinding, at 7. The higher concentration of impurities in the head 5 isdenoted by cross-shading.

A pointed electrode 8 positioned on the semi-conducting body 3 andforming a rectifying connection therewith is welded at 9 to a rod 10,which, similar to the base 1, is provided with a supply conductor 11.The rods 1 and 10 are secured by means of solder 12 in a holderconstituted by a glass tube 13 which has sealed in it two aligned metaltubes 14 made, for example, of ferrochromium.

It will be appreciated that the invention is not limited to thearrangement of the base 1 and the pointed electrode 8 as shown in thedrawing, nor to electrode systems comprising a single pointed electrode,but will be applicable also to three or four electrode systems, such astransistors and the like.

What is claimed is:

1. A semi-conductor device comprising a granular, eggshaped,semi-conductive body of which the narrow head has a greaterconcentration of impurities than the opposite end, said opposite endhaving a planar portion, means effecting a rectifying connection at theplanar portion, and means effecting an ohmic connection at the narrowhead.

2. A device as set forth in claim 1 wherein the semiconductive bodycomprises an element selected from the group consisting of germanium andsilicon.

References Cited in the file of this patent UNITED STATES PATENTS2,572,993 Douglas et a1. Oct. 30, 1951 2,603,692 Scatf et a1 July 15,1952 2,666,874 Barton Jan. 19, 1954 2,723,370 Bradshaw et al Nov. 8,1955 FOREIGN PATENTS 683,248 Great Britain Nov. 26, 1952

1. A SEMI-CONDUCTOR DEVICE COMPRISING A GRANULAR, EGGSHAPED,SEMI-CONDUCTIVE BODY OF WHICH THE NARROW HEAD HAS A GREATERCONCENTRATION OF IMPURITIES THAN THE OPPOSITE END, SAID OPPOSITE ENDHAVING A PLANAR PORTION, MEANS EFFECTING A RECTIFYING CONNECTION AT THEPLANAR PORTION, AND MEANS EFFECTING AN OHMIC CONNECTION AT THE NARROWHEAD.